Embodiments presented herein relate generally to aerodynamic surfaces, and more specifically to configuration of an aerodynamic surface, such as an airfoil, that is resistant to high surface strains experienced during foreign object impacts.
Turbines include, but are not limited to, gas and steam turbine power generation equipment and gas turbine aircraft engines. A turbine engine typically includes a core engine having a high pressure compressor to compress the air flow entering the core engine, a combustor in which a mixture of fuel and compressed air is burned to generate a propulsive gas flow, and a high pressure turbine which is rotated by the propulsive gas flow and which is connected by a larger diameter shaft to drive the high pressure compressor. A typical front fan gas turbine engine adds a low-pressure turbine (located aft of the high pressure turbine) which is connected by a smaller diameter coaxial shaft to drive the front fan (located forward of the high pressure compressor). The low-pressure compressor is sometimes called a booster compressor or simply a booster.
The fan and the high and low pressure compressor of turbine engines have turbine blades each including an airfoil portion attached to a shank or dovetail portion. Conventional gas turbine blade designs typically have airfoil portions that are made entirely of metal, such as titanium, or are made entirely of continuous fiber reinforced composites (CFRC). The all-metal blades are heavier in weight which results in lower fuel performance and requires sturdier blade attachments, while the lighter all-composite blades are more susceptible to damage from foreign object impacts, such as bird ingestion events. Known hybrid blades include a composite blade having an airfoil shape which is covered by a surface cladding (with only the blade tip and the leading and trailing edge portions of the surface cladding comprising a metal) for erosion and foreign object impacts. The gas turbine fan blades typically are the largest (and therefore the heaviest) blades in a gas turbine aircraft engine and the front fan blades are the first to be impacted by a bird strike. Composite blades have typically been used in applications where weight is a major concern. However, composite blades due to their thinness may develop high strain regions in the blade that may be susceptible to failure during foreign object impact. To lower the strain levels in the blades, it is desirable to change the dynamic response of the composite blade.
Accordingly, there is a need for an improved fan blade that provides a lightweight airfoil that is resistant to high airfoil surface strains experienced during foreign object impacts.